Arene cis-dihydrodiols-useful precursors for the preparation of antimetabolites of the shikimic acid pathway: application to the synthesis of 6,6-difluoroshikimic acid and (6S)-6-fluoroshikimic acid

Article abstract of DOI:10.1016/j.tet.2006.03.029

The synthesis of 6,6-difluoroshikimic acid (11) has been achieved in ten steps from the enantiopure diol 16, which is derived from enzymatic cis-dihydroxylation of iodobenzene. The versatility of the synthetic strategy has been demonstrated by the preparation of the known antimicrobial agent, (6S)-6-fluoroshikimic acid (5).

Full text of DOI:10.1016/j.tet.2006.03.029

Tetrahedron 62 (2006) 5099–5108
Arene cis-dihydrodiols—useful precursors for the preparation
of antimetabolites of the shikimic acid pathway: application
to the synthesis of 6,6-difluoroshikimic acid and
(6S)-6-fluoroshikimic acid
*
Jane L. Humphreys, David J. Lowes, Karen A. Wesson and Roger C. Whitehead
School of Chemistry, The University of Manchester, Oxford Road, Manchester M13 9PL, UK
Received 29 September 2004; revised 16 February 2006; accepted 10 March 2006
Available online 5 April 2006
Abstract—The synthesis of 6,6-difluoroshikimic acid (11) has been achieved in ten steps from the enantiopure diol 16, which is derived from
enzymatic cis-dihydroxylation of iodobenzene. The versatility of the synthetic strategy has been demonstrated by the preparation of the known
antimicrobial agent, (6S)-6-fluoroshikimic acid (5).
Ó 2006 Elsevier Ltd. All rights reserved.
CO2H
1
CO2H
1. Introduction
2
6
5
shikimate
kinase
3
Over recent years, there has been extensive interest in the
efficient preparation of analogues of (ꢀ)-shikimic acid (1),
which have been targeted as likely inhibitors of enzymes
on the shikimic acid pathway and which are of relevance
as potential antifungal, antibacterial and antiparasitic agents.
A principal goal of our present research is the synthesis of
analogues of (1), which may either inhibit shikimate kinase,
or alternatively undergo intracellular phosphorylation by the
kinase and thereby act as prodrugs for inhibitors of enzymes
further downstream on the pathway (e.g., EPSP synthase or
chorismate synthase (Scheme 1)).1
4
HO
OH
P O
OH
OH
OH
shikimic acid
shikimic acid-3-
phosphate
1
2
EPSP
synthase
CO2H
CO2H
chorismate
synthase
O
CO2H
P O
O
CO2H
OH
OH
The feasibility of this approach is supported by the findings
of extensive studies of the fluorinated analogues 5 and 6 of
(ꢀ)-shikimic acid (1) (Scheme 2).2 Both of these compounds
display in vitro antibacterial activity against a range of
Escherichia coli strains with (6S)-6-fluoroshikimic acid (5)
being the more potent agent (MIC against E. coli K-12 of
0.1 mg/mL compared with 64 mg/mL for (6R)-6-fluoroshiki-
mic acid (6)).3 The fluorinated analogues are substrates for
the shikimate transport system of E. coli4 and importantly,
the (6S)-isomer 5 has been shown to be protective against
a range of bacterial intraperitoneal challenges in mice.3
Both compounds are substrates for shikimate kinase from
E. coli and are transformed to the corresponding 6-fluoro-
chorismic acid
5-enolpyruvyl-shikimic
acid-3-phosphate
(EPSP)
4
3
Scheme 1.
shikimate-3-phosphates 7 and 8 at rates comparable to
(ꢀ)-shikimic acid itself. In turn, compounds 7 and 8 are
transformed by EPSP synthase from E. coli to the corre-
sponding 6-fluoro-EPSP analogues 9 and 10 at rates approx-
imately one order of magnitude slower than the natural
substrate.5 Further studies have indicated that the antimicro-
bial activity of 6 is due, at least in part, to ultimate inhibition
of chorismate synthase whereas 5 is proposed to act via ulti-
mate inhibition of 4-amino-4-deoxychorismate synthase
(ADCS), an enzyme on the post-chorismate branch of the
pathway leading to para-aminobenzoic acid (PABA).6
Keywords: Shikimic acid; Fluorination; Antibacterial agents.
* Corresponding author. Tel.: +44 161 275 7856; fax: +44 161 275 4939;
e-mail: roger.whitehead@manchester.ac.uk
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.03.029

5100
J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
ment with the nucleophilic fluorinating agent [bis-(2-
methoxyethyl)]-aminosulfurtrifluoride (DeoxoFluorÒ)8 was
converted to the gem-difluoride 14. Unfortunately, all
attempts to introduce a carboxyl substituent at C1 of 14
using Pd(0) chemistry, as well as using other trans-metall-
ation protocols, were unsuccessful.
It is well documented that aryl and vinyl bromides exhibit
diminished reactivity in Pd(0) catalysed C–C bond forming
reactions when compared with the corresponding vinyl
iodides. We decided, therefore, to turn our attention to the
preparation of the analogue of 14, which bears an iodine
atom at C1. Our starting material for this synthesis was the
enantiomerically pure diol 16, which is obtained from the
toluene-dioxygenase catalysed cis-dihydroxylation of iodo-
benzene (Scheme 4).9,10
Scheme 2.
I
I
O
It has been disclosed quite recently that both 5 and 6 inhibit
the growth of the parasite Plasmodium falciparum, the prin-
cipal causative agent of malaria in humans.7 In contrast to the
situation with E. coli, the (6R)-compound 6 was significantly
more potent than isomer 5 in this assay. This intriguing dis-
covery has stimulated renewed interest in the design and syn-
thesis of novel inhibitors of enzymes on the shikimate
pathway. In this paper, we provide details of the synthesis
of compound 11, the final member of the series of 6-fluoro-
shikimic acids (Fig. 1). We also describe our investigations
into modifications of the synthetic approach for the prepara-
tion of other 6-substituted analogues of (ꢀ)-shikimic acid.
i), ii)
OH
OH
O
HO
OH
17
16
iii)
I
I
O
O
O
iv)
4
O
BnO
BnO
OAc
19
OH
18
Scheme 4. Reagents: (i) (CH3O)2C(CH3)2, p-TSA, CH2Cl2; (ii) OsO4 (cat.),
NMO, tBuOH, H2O, 81% over two steps; (iii) Bu2SnO, C6H5CH3, CH3OH,
D, then BnBr, Bu4NI, C6H5CH3, 130 ꢁC, 91%; (iv) Ac2O, DMAP, py,
CH2Cl2, quant.
CO2H
F
F
HO
OH
Following the general procedure of Hudlicky,11 the vicinal
diol in 16 was protected as an acetonide and subsequent
face-selective cis-dihydroxylation of the less substituted
3,4-double bond gave diol 17 in good yield. Using the excel-
lent protocol reported recently by Simas and co-workers,12
a high-yielding and regioselective mono-benzylation of the
vicinal diol in 17 was accomplished via an intermediate stan-
nylene acetal, to give the benzyl ether 18.13 The regioselec-
tivity of this reaction was confirmed by acetylation of the
remaining free hydroxyl of 18 to give 19: comparison of
the 1H NMR spectra of the two compounds confirmed a sig-
nificant downfield shift of the resonance assigned to C(4)H
in compound 19 [dH (300 MHz; CDCl3): w4.41 for 18,
5.53 for 19].
OH
11
Figure 1.
2. Results and discussion
Quite recently, we reported details of the synthesis of vinyl
bromide 13 in four steps from commercially available diol
12 (Scheme 3).1a Oxidation of the allylic hydroxyl in 13
gave the expected a,b-unsaturated ketone which, on treat-
Br
Br
OH
O
O
O
BnO
HO
Over recent years, the protection of substrates bearing vici-
nal di-equatorial hydroxyl groups as their butane-diacetal
(BDA) derivatives, has received a great deal of attention.14
The enhanced stability of compounds protected in this way
permits the use of a wide variety of reagents and conditions
and furthermore, their conformational rigidity often has
a beneficial influence on the stereoselectivity of subsequent
transformations. Prompted by these observations, we initi-
ated investigations into the conversion of 18 into the BDA
protected compound 20, which we believed would be a
robust and versatile intermediate, not only for the synthesis
of our target compound 11 but also for other analogues of
(ꢀ)-shikimic acid (Scheme 5).
OCH3
O
OH
H3CO
12
13
CO2CH3
F
Br
O
F
F
F
X
O
O
O
BnO
BnO
OCH3
OCH3
H3CO
H3CO
15
14
Scheme 3.

J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
5101
I
I
1
6
2
F
F
O
5
3
4
O
BnO
O
BnO
OCH3
I
OH
O
18
O
O
i)
H3CO
i), ii)
23
+
I
or
ii)
X
BnO
O
OCH3
F
H3CO
I
21
F
OH
O
BnO
OCH3
O
BnO
O
OCH3
H3CO
24
O
H3CO
Scheme 6. Reagents: (i) DeoxoFluorÒ, rt, 72 h, 30% of 23, 36% of 24.
20
iv)
iii)
Br
I
I
I
OSF2NR2
F
F
F
O
O
OCOPh
O
O
BnO
BnO
BnO
BnO
O
OCH3
OCH3
OCH3
OCH3
O
O
O
O
H3CO
H3CO
25
26
H3CO
H3CO
21
22
Figure 2.
Scheme 5. Reagents: (i) TFA/H2O (1:1), rt; (ii) butan-2,3-dione,
(CH3O)3CH, CSA, CH3OH, D; (iii) DMSO, (COCl)2, Et3N, CH2Cl2,
ꢀ78 ꢁC to rt, 15% over two steps; 36% over three steps; (iv) Ph3P, DIAD,
C6H5CO2H, THF, 49% over three steps.
Previous research efforts in our group have culminated in the
development of mild reaction conditions for the isomerisa-
tion of the allylic fluoride 27 to the gem-difluoride 29
(Scheme 7).17 In this model system, it transpired that simply
Direct trans-ketalisation of 18 with butan-2,3-dione gave an
inseparable mixture of diacetals consisting predominantly of
the desired isomer 20. This mixture was then oxidised using
Swern conditions15 to give 21 in a disappointing 15% yield
over two steps. A lengthier three-step procedure was thus
developed, involving acid-catalysed hydrolysis of 18 to give
the corresponding triol, followed by ketalisation to give an
inseparable mixture of diacetals, which mostly comprised
the desired isomer 20. Oxidation of this mixture followed
by chromatographic purification provided the enone 21 in
an acceptable yield of 36% over three steps. Derivatisation
of the inseparable mixture of diacetals with acetic anhydride
and pyridine did not facilitate the purification of compound
20 (as the (6S)-acetate), however, exposure of the mixture of
diacetals to Mitsunobu conditions16 allowed isolation of the
(6R)-benzoate 22 in 49% yield over three steps from 18.
˚
stirring a solution of 27 in CH2Cl2 in the presence of 4 A
molecular sieves resulted in quantitative conversion of 27
to 29. We have not carried out detailed investigations into
the mechanism of this intriguing transformation, however,
the reaction is presumed to proceed via the intermediacy
of a transient allylic carbenium ion 28. Unfortunately, de-
spite extensive investigations, it proved impossible to dis-
cover conditions under which allylic fluoride 23 could be
isomerised to gem-difluoride 24. The contrasting reactivity
of 23 and 27 is presumed to reflect the instability of the
highly oxygenated carbenium ion, which is considered to
be a necessary intermediate in the isomerisation of 23.
I
I
I
F
F
With the pivotal enone 21 in hand, we were able to investi-
gate the key fluorodeoxygenation step necessary for the
introduction of geminal fluorines at C6. Treatment of 21
with DeoxoFluorÒ in the absence of additional solvent for
72 h resulted in the formation of two isomeric difluorides.
After chromatographic purification, the desired gem-difluo-
ride 24 was isolated in 36% yield and the isomeric allylic
fluoride 23 was isolated in 30% yield (Scheme 6).
F
F
F
+
27
28
29
˚
Scheme 7. Reagents: (i) 4 A mol. sieves, CH2Cl2, rt, 8 h, quant.
Having successfully prepared the gem-difluoride 24, we
were in a position to investigate the key carbonylation reac-
tion: the transformation that had thwarted progress in the
corresponding vinyl bromide series.1a Previous model stud-
ies indicated that the vinyl iodide 29 was an excellent sub-
strate in a variety of Pd(0)-mediated transformations. In
particular, carbonylation using conditions modified from
The configuration at C6 of 23 was confirmed by comparison
of its spectroscopic data with those of the corresponding
vinyl bromide 25 (Fig. 2), the structure of which was previ-
ously assigned by the use of 2D heteronuclear Overhauser
effect spectroscopy (HOESY).1a The formation of 23 is
presumed to occur via allylic rearrangement during the
difluorination reaction and the observed regiochemical
outcome is likely to be a consequence of either a SN20 or
a SN10 reaction of an activated intermediate of type 26
with ambient fluoride ion.
those described by Ortar18 (tri-2-furyl phosphine and Hunigs
¨
base replacing triphenylphosphine and triethylamine,
respectively) gave the corresponding unsaturated ester in
55% yield. Pleasingly, application of these reaction condi-
tions to 24 yielded the desired ester 30 in comparable yield
(56%) (Scheme 8).

5102
J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
I
CO2CH3
F
CO2CH3
CO2H
F
i)
i)
F
F
O
O
HO
OH
OH
32
BnO
BnO
H3CO
HO
OH
OCH3
OCH3
O
O
OH
1
H3CO
30
24
ii)
I
CO2CH3
F
CO2H
CO2H
F
F
F
X
+
HO
+
OH
1
O
O
O
BnO
H3CO
BnO
OCH3
OCH3
O
OH
34
OH
33
H3CO
31
23
Scheme 9. Reagents: (i) concd HCl/H2O (1:1), 60–70 ꢁC, 12 h, 86%; (ii)
concd HCl/H2O (1:1), 100 ꢁC, 30 h.
Scheme 8. Reagents: (i) Pd(OAc)2, diisopropylethylamine, tri-2-furylphos-
phine, CH3OH, CO, DMF, rt, 24 h, 56%.
Exposure of the allylic rearrangement product 23 to the same
carbonylation conditions failed to provide any of the
expected unsaturated ester 31 and, indeed, starting material
remained unchanged. This finding was particularly disap-
pointing as we had envisaged that in the presence of fluoride
ion, compound 31 might undergo relatively facile rearrange-
ment to the gem-difluoride 30 via a conjugate addition–elim-
ination sequence.
CO2CH3
F
CO2CH3
F
CO2H
F
i)
ii)
HO
F
F
OH
F
O
O
BnO
BnO
OH
OCH3
OH
OH
H3CO
30
35
11
Scheme 10. Reagents: (i) TFA/H2O (6:1), rt, 3 h; (ii) concd. HCl/H2O (1:1),
60–70 ꢁC, 12 h then HPLC, 68% over two steps.
The successful preparation of unsaturated ester 30 meant that
all that remained to be accomplished was complete deprotec-
tion to give the target material 11. Several plausible
sequences were considered with the main requirement being
for conditions that would allow efficient removal of the ben-
zyl protecting group without recourse to hydrogenolysis
procedures. The possibility of effecting ester hydrolysis
and concomitant debenzylation under acidic conditions
was particularly attractive, however, we were cognizant of
the pioneering work of J. F. Eykmann.19 During his classic
structural and reactivity studies of (ꢀ)-shikimic acid, Eyk-
mann observed that the natural material underwent facile
dehydrative aromatisation when heated in hydrochloric acid
to give para-hydroxy benzoic acid. With a view to discover-
ing reaction conditions under which aromatisation could be
minimised, we carried out a brief investigation into the fate
of methyl shikimate (32) when heated at different tempera-
tures inw6 M HCl. In accord with Eykmann’s observations,
heating 32 at 100 ꢁC inw6 M HCl for 30 h resulted in partial
conversion to para-hydroxy benzoic acid 33. A substantial
quantity of 3-epi-shikimic acid (34) and a lesser quantity
of 1 itself were also formed in the reaction (crude ratio
33:34:1 was 2:2:1). When the reaction time was shortened
to 12 h, the product mixture was more complicated and anal-
ysis by 1H NMR indicated the presence of other ‘shikimate-
like’ materials as well as 33, 34 and 1 (crude ratio 33:34:1
was 2:6:9). In contrast, when the temperature was decreased
tow60 ꢁC and the reaction time maintained at 12 h, analysis
of the crude reaction mixture indicated that no aromatisation
or epimerisation had taken place and the only isolable prod-
uct was (ꢀ)-shikimic acid (1) (Scheme 9).
water (6:1) at room temperature. Secondly, in accord with
our model studies, removal of the benzyl protecting group
and concomitant ester hydrolysis was accomplished by heat-
ing a solution of the diol 35 in w6 M HCl at 60–70 ꢁC for
12 h. Analysis of the crude product from this sequence by
1H NMR spectroscopy indicated that no aromatisation had
occurred and the target compound 11 was generated in
essentially pure form.
The shikimic acid pathway is a wonderful and elegant
example of a divergent biosynthetic sequence: a plethora of
aromatic end products is derived from a single, pre-branch-
point intermediate of the pathway, chorismic acid (4).21,22
Taking our lead from this impressive biosynthetic example,
a major goal of our recent endeavours has been the develop-
ment of a divergent synthetic strategy which will allow the
efficient preparation of a range of analogues of shikimic
acid. In this context, we envisaged vinyl iodide 20 (or an
alternatively protected variant of 20) to be a pivotal interme-
diate, however, high-yielding preparation of a sample of this
compound had not been possible from the acetonide 18 (vide
supra). During the course of our investigations, however, we
became aware of the ‘aromatic Finkelstein reaction’ devel-
oped by Buchwald and co-workers.23 This incredibly useful
reaction effects the conversion of aryl bromides to the corre-
sponding aryl iodides by the action of a catalytic quantity of
CuI, KI and a 1,2-diamine additive. In the original publica-
tion, a single example of a halogen exchange of a vinyl bro-
mide was reported and this prompted us to carry out a brief
investigation into the halogen exchange of vinyl bromide
38. This simple compound was readily prepared in two steps
from 2-cyclohexenone (36)24,25 and was selected as an
appropriate model for the highly oxygenated vinyl bromide
13 (Scheme 11).
Encouraged by these observations, as well as the literature
precedent for the cleavage of benzyl ethers under acidic con-
ditions,20 we embarked on the final deprotection sequence to
give 11. Ultimately, this was achieved in two straightforward
steps (Scheme 10). Firstly, the BDA group was removed in
quantitative fashion by stirring 30 in a mixture of TFA and
Reaction of 38 under the conditions described by Buchwald
resulted in generation of crude product mixtures consisting

J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
5103
Br
furnished (6S)-6-fluoroshikimic acid (5), which was identi-
cal in all respects to an authentic sample kindly provided
by AstraZeneca.
O
O
i)
36
37
ii)
3. Conclusions
Br
I
In summary, we have prepared the novel compound, 6,6-
difluoroshikimic acid (11), in ten steps from the enantiopure
diol 16. A key step in the synthesis, fluorodeoxygenation of
enone 21, was accomplished using the nucleophilic fluori-
nating agent DeoxoFluorÒ: although the total yield of
difluorinated products from this reaction was reasonable,
competing mechanistic processes resulted in the generation
of only moderate quantities of the required gem-difluori-
nated product 24 together with equivalent amounts of an
undesired vinyl fluoride 23, arising from allylic rearrange-
ment. In contrast to previous model studies, it proved impos-
sible to isomerise the latter compound to gem-difluoride 24,
thus making the fluorine incorporation step the least efficient
of the sequence.
OH
OH
iii)
38
39
Scheme 11. Reagents: (i) Br2, Et3N, CH2Cl2, 0 ꢁC to rt, 65%; (ii) NaBH4,
CeCl3, CH3OH, rt, 90%; (iii) KI, CuI, N,N0-dimethylethylenediamine,
nBuOH, 130 ꢁC, 24 h.
1
predominantly of vinyl iodide 39 (ratios assessed by H
NMR analysis). In our hands, the reaction was a little capri-
cious and ratios of 39:38 generally varied unpredictably
between 4:1 and 14:1. Interestingly, when the 1,2-diamine
additive, N,N0-dimethylethylenediamine, was replaced with
trans-1,2-diaminocyclohexane, the outcome was much infe-
rior and ratios of 39:38 ranging from 1:3 to 1:7 were com-
monly obtained. The relative success of the conversion of
38 to 39 using N,N0-dimethylethylenediamine, encouraged
us to attempt the halogen exchange of vinyl bromide 13.
Pleasingly, application of the conditions used in the model
study resulted in good conversion to the vinyl iodide 20
(<10% contamination by 13) (Scheme 12).
Allylic alcohol 20, an intermediate in the synthesis of 6,6-
difluoroshikimic acid, was selected as an ideal candidate
for a diversification point for the synthesis of other ana-
logues of (ꢀ)-shikimic acid. Although not directly accessi-
ble in pure form from enantiopure diol 16, compound 20
has been synthesised from the analogous vinyl bromide 13
via application of Buchwald’s ‘aromatic Finkelstein reac-
tion’. The potential synthetic utility of 20 has been demon-
strated by the preparation of the known antibacterial agent
(6S)-6-fluoroshikimic acid (5).
Br
I
OH
O
OH
O
i)
BnO
BnO
OCH3
OCH3
O
O
H3CO
H3CO
13
20
4. Experimental
4.1. General
ii)
CO2CH3
F
I
F
Solvents were dried and distilled before use. Chromato-
graphy was performed over Merck silica gel 60 (40–
63 mm). IR spectra were recorded on a Perkin–Elmer 881
spectrometer or an AT1-Mattson Genesis Series FTIR spec-
iii)
O
O
O
BnO
BnO
OCH3
OCH3
O
H3CO
H3CO
1
trometer. H, 13C and 19F NMR spectra were recorded on
41
40
iv)
a Varian Inova 400 MHz spectrometer or a Varian Inova
300 MHz spectrometer. Chemical shifts are referenced to
the residual solvent peak. Mass spectra were recorded on
Fisons VG Trio 2000 quadrupole (EI/CI, low resolution),
Kratos Concept 1S (EI/CI, high resolution) and Micromass
Platform (electrospray) spectrometers.
CO2CH3
F
CO2H
F
v)
OH
OH
BnO
HO
OH
OH
42
5
4.1.1. (3R,4R,5S,6S)-1-Iodo-5-O,6-O-(propane-20,20-
diyl)-cyclohex-1-ene-3,4,5,6-tetraol (17). To a stirred solu-
tion of (5S,6S)-1-iodo-5,6-dihydroxycyclohexa-1,3-diene
(16) (1.109 g, 4.66 mmol) in CH2Cl2 (36 mL) was added
2,2-dimethoxypropane (0.63 mL, 5.13 mmol) and a catalytic
quantity of p-TSA. The reaction mixture was stirred at room
temperature for 1 h after which time it was quenched by the
addition of a saturated aqueous solution of sodium bicarbon-
ate (40 mL). The organic phase was collected and combined
with three further CH2Cl2 extracts (3ꢂ40 mL). The com-
bined organic extracts were dried (MgSO4) and concentrated
in vacuo to provide the crude acetonide as a pale yellow oil
Scheme 12. Reagents: (i) CuI, KI, N,N0-dimethylethylenediamine, nBuOH,
130 ꢁC; (ii) Et2NSF3, CH2Cl2, ꢀ78 ꢁC to rt, 38% over two steps from 13;
(iii) Pd(OAc)2, diisopropylethylamine, tri-2-furylphosphine, CH3OH, CO,
DMF, rt, 24 h, 58%; (iv) TFA/H2O (6:1), rt, 3 h, 72%; (v) concd HCl/H2O
(1:1), 60–70 ꢁC, 10 h then HPLC, 61%.
Subsequent fluorodeoxygenation of 20 using the nucleo-
philic fluorinating agent DAST (Et2NSF3)26 proceeded
with inversion of configuration to give the allylic fluoride
40, which could be obtained free of the corresponding vinyl
bromide after chromatographic purification. Pd(0) mediated
carbonylation of 40 occurred in comparable yield to the
difluorinated analogue 24, to give the a,b-unsaturated ester
41 and finally, two-stage removal of the protecting groups
t
(1.203 g). This material was dissolved in BuOH (15 mL)
and N-methylmorpholine-N-oxide (0.56 g, 4.76 mmol) was

5104
J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
added followed by a solution of OsO4 in tBuOH (1.8 mL of
a 2.5% solution) and water (a few drops). The reaction mix-
ture was stirred at room temperature for 36 h under an atmo-
sphere of nitrogen when it was quenched by the addition of
solid sodium metabisulphite (1.97 g) and filtered through
a pad of silica, eluting with EtOAc. Concentration of the fil-
trate invacuo gave the crude product as a dark-coloured solid,
which was purified by flash column chromatography (SiO2;
EtOAc/petroleum ether (40–60), 7:13) to give the title com-
pound as colourless crystals (1.175 g, 81%). Rf 0.41 (EtOAc/
petroleum ether (40–60), 2:5); mp 146–148 ꢁC; [a]D27 +23.6
(c 0.78, CH2Cl2); nmax (film)/cmꢀ1 3502s and 3376s (O–H),
2923w and 2882w (C–H), 1631w (C]C); dH (300 MHz;
CDCl3) 1.38 and 1.41 (2ꢂ3H, 2ꢂs, 2ꢂacetonide CH3), 2.5
(2H, br, OH), 4.21 (1H, wt, J 4.4, C(4)H), 4.28–4.33 (1H,
m, C(3)H), 4.38 (1H, t, J 5.2, C(5)H), 4.63 (1H, br d, J 5.2,
C(6)H), 6.41 (1H, d, J 3.0, C(2)H); dC (75 MHz; CDCl3)
26.5 and 27.9 (2ꢂacetonide CH3), 67.9 (C(3)H), 69.5
(C(4)H), 76.4 (C(5)H), 78.6 (C(6)H), 100.8 (C(1)), 110.2
(acetonide C), 139.2 (C(2)H); m/z (EI) 312 (M+, 3%), 297
(12), 254 (12), 127 (15), 109 (68), 101 (100) (Found
311.9853, C9H13IO4 (M+) requires 311.9860).
reaction mixture was quenched by the addition of a saturated
aqueous solution of ammonium chloride (10 mL). Organic
material was extracted into CH2Cl2 (3ꢂ10 mL) and the
combined extracts were dried (MgSO4) and concentrated
in vacuo to give the product 19 as a viscous oil, which was
of sufficient purity for spectroscopic analysis. nmax (film)/
cmꢀ1 2986w, 2932w and 2870w (C–H), 1747s (C]O); dH
(300 MHz; CDCl3) 1.37 and 1.40 (2ꢂ3H, 2ꢂs, 2ꢂacetonide
CH3), 2.09 (3H, s, OC(]O)CH3), 4.14 (1H, td, J 3.5, 1.5,
C(3)H), 4.39 (1H, t, J 5.5, C(5)H), 4.51 (1H, d, J 11.7,
OCHaHbPh), 4.62 (1H, d, J 11.7, OCHaHbPh), 4.64 (1H, d,
J 5.5, C(6)H), 5.53 (1H, dd, J 5.5, 3.5, C(4)H), 6.48 (1H,
br d, J 3.5, C(2)H), 7.26–7.34 (5H, m, aromatic CH); dC
(75.4 MHz; CDCl3) 21.3 (OC(]O)CH3), 26.4 and 27.8
(2ꢂacetonide CH3), 69.2 (C(4)H), 72.1 (benzyl CH2), 73.3
(C(3)H), 74.2 (C(5)H), 79.0 (C(6)H), 100.1 (C(1)), 110.4
(acetonide C), 128.1, 128.3 and 128.8 (aromatic CH),
137.8 (aromatic ipso-C), 138.6 (C(2)H), 170.6 (C]O); m/z
(CI/NH3) 462 (MNH+4, 60%), 445 (MH+, 25), 336 (100)
(Found 462.0779, C18H25INO5 (MNH+4) requires 462.0778).
4.1.4. (20S,30S,4R,5R,6S)-2-Iodo-4-O-benzyl-5-O,6-O-
(20,30-dimethoxybutane-20,30-diyl)-cyclohex-2-ene-1-one-
4,5,6-triol (21). A solution of alcohol 18 (0.290 g,
0.72 mmol) in a 1:1 mixture of water and TFA (12 mL)
was stirred at room temperature for 3 h and the residual
solvents were then removed directly in vacuo to give the
intermediate triol in quantitative yield. This material was
dissolved in dry methanol (7 mL) under an atmosphere of
nitrogen and to the stirred solution were added CSA (a few
crystals), trimethylorthoformate (1.6 mL, 14.4 mmol) and
2,3-butandione (0.14 mL, 1.56 mmol). The reaction mixture
was then heated at reflux for 24 h, during which time it
developed a deep red colouration. It was then allowed to
cool to room temperature and Et3N (0.2 mL, 1.4 mmol)
was added. Residual solvents were then removed in vacuo
and the crude product was partially purified by flash column
chromatography (SiO2; EtOAc/petroleum ether (40–60),
1:9), to give a mixture of compounds consisting predomi-
nantly of the desired isomer 20 (0.256 g).
4.1.2. (3R,4R,5S,6S)-1-Iodo-3-O-benzyl-5-O,6-O-(pro-
pane-20,20-diyl)-cyclohex-1-ene-3,4,5,6-tetraol (18).
A
solution of the diol 17 (0.245 g, 0.79 mmol) and Bu2SnO
(0.236 g, 0.95 mmol) in a 1:1 mixture of methanol and tolu-
ene (4 mL) was heated at 130 ꢁC for 3 h. After this time, the
solvent was evaporated under reduced pressure. Dry toluene
(4 mL) was added and then evaporated under reduced pres-
sure. The resulting crude stannylene acetal was redissolved
in toluene (4 mL) and Bu4NBr (0.058 g, 0.16 mmol) and
BnBr (0.19 mL, 1.58 mmol) were added. The mixture was
then heated at 130 ꢁC under an atmosphere of nitrogen for
6 h whereafter the solvent was removed in vacuo to give
the crude product as a yellow oil. Purification by flash
column chromatography (SiO2; EtOAc/petroleum ether
(40–60), 3:17), using a pad of KF at the top of the column
to remove tin residues gave the title compound as colourless
crystals (0.290 g, 91%). Rf 0.32 (EtOAc/petroleum ether
(40–60), 3:17); mp 73–74 ꢁC; [a]D22 ꢀ28.5 (c 1.20,
CH2Cl2); nmax (film)/cmꢀ1 3464br (O–H), 2985m and
2890m (C–H), 1630w (C]C); dH (300 MHz; CDCl3) 1.42
and 1.43 (2ꢂ3H, 2ꢂs, 2ꢂacetonide CH3), 2.51 (1H, d, J
2.3, OH), 4.13 (1H, dd, J 4.1, 3.6, C(3)H), 4.40–4.43 (1H,
m, C(4)H), 4.45 (1H, t, J 4.8, C(5)H), 4.64–4.73 (3H, m,
C(6)H and benzyl CH2), 6.46 (1H, d, J 3.6, C(2)H), 7.34–
7.45 (5H, m, aromatic CH); dC (75 MHz; CDCl3) 26.5 and
27.8 (2ꢂacetonide CH3), 67.5 (C(4)H), 71.9 (benzyl CH2),
75.0 (C(3)H), 76.1 (C(5)H), 78.5 (C(6)H), 101.5 (C(1)),
110.1 (acetonide C), 128.1, 128.5 and 128.9 (aromatic CH),
136.8 (C(2)H), 137.5 (aromatic ipso-C); m/z (CI/NH3) 420
(MNH+4, 40%), 403 (MH+, 35), 294 (60), 277 (25), 106
(45), 58 (100) (Found 420.0674, C16H23INO4 (MNH+4)
requires 420.0672).
A solution of DMSO (0.05 mL, 0.70 mmol) in CH2Cl2
(2.5 mL) was added dropwise, under an atmosphere of nitro-
gen, to a solution of oxalyl chloride (0.06 mL, 0.69 mmol) in
CH2Cl2 (2.5 mL), maintaining the reaction temperature
below ꢀ60 ꢁC. The reaction mixture was stirred for 30 min
at <ꢀ60 ꢁC, before a pre-cooled solution of the crude bis-
acetal 20 (0.256 g) in CH2Cl2 (3.5 mL) was added dropwise.
The reaction mixture was stirred below ꢀ60 ꢁC for a further
65 min before Et3N (0.34 mL, 2.43 mmol) was added drop-
wise and the resulting yellow solution was allowed to
warm gradually to room temperature. After stirring for a
further 4 h at room temperature, the reaction mixture was
quenched by the addition of a saturated aqueous solution of
ammonium chloride (150 mL). The organic phase was col-
lected and combined with three further CH2Cl2 extracts
(3ꢂ100 mL). The combined organic extracts were dried
(MgSO4) and concentrated in vacuo. Purification by flash
column chromatography (SiO2; EtOAc/petroleum ether
(40–60), 1:12) gave the title compound as a viscous oil
(0.125 g, 36% from 18). Rf 0.16 (EtOAc/petroleum ether
(40–60), 1:19); [a]2D7 ꢀ7.70 (c 1.03, CH2Cl2); nmax (film)/
cmꢀ1 2924m (C–H), 1711s (C]O); dH (300 MHz; CDCl3)
4.1.3. (3R,4R,5S,6S)-1-Iodo-3-O-benzyl-4-O-acetyl-5-
O,6-O-(propane-20,20-diyl)-cyclohex-1-ene-3,4,5,6-tetraol
(19). To a stirred solution of the benzyl ether 18 (0.04 g,
0.1 mmol) and DMAP (a few crystals) in CH2Cl2 (1 mL),
under an atmosphere of nitrogen, was added acetic anhy-
dride (0.5 mL, 5.3 mmol) followed by pyridine (0.5 mL,
6.2 mmol). After stirring at room temperature for 6 h, the

J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
5105
1.43 and 1.46 (2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.31 and 3.38
(2ꢂ3H, 2ꢂs, 2ꢂacetal OCH3), 4.11 (1H, dd, J 10.8, 3.5,
C(5)H), 4.24 (1H, dd, J 6.4, 3.5, C(4)H), 4.72 (1H, d, J
11.3, OCHaHbPh), 5.02 (1H, d, J 10.8, C(6)H), 5.12 (1H, d,
J 11.3, OCHaHbPh), 7.35–7.52 (5H, m, aromatic CH), 7.59
(1H, d, J 6.4, C(3)H); dC (75.4 MHz; CDCl3) 17.88 and
17.90 (2ꢂbutyl CH3), 48.4 and 48.7 (2ꢂacetal OCH3), 69.2
(C(6)H), 69.7 (C(5)H), 73.7 (C(4)H), 74.4 (benzyl CH2),
99.7 and 100.4 (2ꢂacetal C), 107.3 (C(2)), 128.4, 128.6
and 128.8 (aromatic CH), 138.3 (aromatic ipso-C), 151.3
(C(3)H), 186.4 (C]O); m/z (CI/NH3) 492 (MNH+4, 32%),
391 (57), 136 (52), 124 (56), 106 (100), 100 (90), 88 (80)
(Found 492.0885, C19H27INO6 (MNH+4) requires 492.0883).
an oil (0.060 g, 36%) and the allylically rearranged isomer
23 also as an oil (0.050 g, 30%). Data for 24: Rf 0.67
(EtOAc/petroleum ether (40–60), 1:4); [a]1D9 +26.1 (c 1.36,
CH2Cl2); nmax (film)/cmꢀ1 2994m, 2957m, 2925m and
2836m (C–H); dH (300 MHz; CDCl3) 1.42 and 1.46
(2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.33 and 3.40 (2ꢂ3H, 2ꢂs,
2ꢂacetal OCH3), 4.01 (1H, dd, J 11.0, 3.7, C(4)H), 4.06
(1H, ddd, J 5.5, 3.7, 1.9, C(3)H), 4.62 (1H, ddd, J 14.7,
11.0, 8.6, C(5)H), 4.67 (1H, d, J 11.1, OCHaHbPh), 5.06
(1H, d, J 11.1, OCHaHbPh), 6.75 (1H, dd, J 5.5, 2.4,
C(2)H), 7.35–7.50 (5H, m, aromatic CH); dC (75.4 MHz;
CDCl3) 17.87 and 17.95 (2ꢂbutyl CH3), 48.47 and 48.48
(2ꢂacetal OCH3), 65.9 (dd, J 23.0, 17.6, C(5)H), 67.3 (d,
J 8.3, C(4)H), 73.4 (C(3)H), 74.4 (benzyl CH2), 97.8 (dd,
J 33.3, 27.9, C(1)), 99.6 and 99.9 (2ꢂacetal C), 115.2 (dd,
J 246.0, 243.3, C(6)F2), 128.2, 128.5 and 128.7 (aromatic
CH), 138.4 (aromatic ipso-C), 142.3 (t, J 7.2, C(2)H); dF
(376.3 MHz; CDCl3) ꢀ104.6 (1F, dd, J 265.3, 14.7, one of
C(6)F2), ꢀ91.6 (1F, ddd, J 265.3, 8.6, 2.4, one of C(6)F2);
m/z (CI/NH3) 514 (MNH+4, 4%), 482 (3), 388 (3), 356 (6),
307 (6), 85 (100) (Found 514.0905, C19H27F2INO5
(MNH+4) requires 514.0896). Data for 23: Rf 0.80 (EtOAc/
petroleum ether (40–60), 1:4); [a]1D9 +84.8 (c 1.0, CH2Cl2);
nmax (film)/cmꢀ1 2993m, 2949m, 2924m and 2834m (C–
H), 1667m (C]C); dH (300 MHz; CDCl3) 1.41 and 1.42
(2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.31 and 3.36 (2ꢂ3H, 2ꢂs,
2ꢂacetal OCH3), 4.04 (1H, dt, J 8.5, 2.3, C(5)H), 4.16
(1H, dt, J 9.0, 2.1, C(4)H), 4.72 (1H, d, J 11.6, OCHaHbPh),
4.88 (1H, ddd, J 11.3, 9.0, 3.7, C(3)H), 5.00 (1H, d, J 11.6,
OCHaHbPh), 5.04 (1H, ddd, 46.7, 6.8, 2.3, C(6)HF), 7.35–
7.43 (5H, m, aromatic CH); dC (75.4 MHz; CDCl3) 17.90
and 17.94 (2ꢂbutyl CH3), 48.4 and 48.5 (2ꢂacetal OCH3),
64.1 (dd, J 21.6, 2.9, C(3)H), 68.2 (d, J 4.1, C(4)H), 70.8
(dd, J 22.4, 21.9, C(1)), 74.0 (benzyl CH2), 76.3 (dd, J
27.3, 1.7, C(5)H), 93.0 (dd, J 182, 7.5, C(6)HF), 100.7
(2ꢂacetal C), 128.3 and 128.8 (aromatic CH), 137.9 (aro-
matic ipso-C), 161.4 (dd, J 279.3, 11.2, C(2)F); dF
(376.3 MHz; CDCl3) ꢀ163.7 (1F, ddddd, J 46.7, 11.3, 8.5,
6.8, 2.0, C(6)HF), ꢀ85.7 (1F, td, J 6.8, 3.7, C(2)F); m/z
(CI/NH3) 514 (MNH+4, 1%), 482 (2), 356 (1), 307 (1), 85
(100) (Found 514.0902, C19H27F2INO5 (MNH+4) requires
514.0896).
4.1.5. (20S,30S,3R,4R,5S,6R)-1-Iodo-3-O-benzyl-4-O,5-O-
(20,30-dimethoxybutane-20,30-diyl)-6-O-benzoyl-cyclo-
hex-1-ene-3,4,5,6-tetraol (22). To a solution of the mixture
of bis-acetals containing 20 prepared as described above
(0.42 g, 0.88 mmol) in THF (8 mL) was added a solution
of triphenylphosphine (0.92 g, 3.52 mmol) in THF
(10 mL) followed by a solution of benzoic acid (0.22 g,
1.76 mmol) in THF (5 mL) and finally diisopropylazodi-
carboxylate (0.35 mL, 1.76 mmol). The reaction mixture
was stirred for 18 h when the solvent was removed in vacuo
to give the crude product as a yellow oil. Purification by flash
column chromatography (SiO2; EtOAc/petroleum ether
(40–60), 1:19) gave the title compound as colourless crystals
(0.440 g, 49% from 18). Rf 0.15 (EtOAc/petroleum ether
(40–60), 1:9); mp 52.9–55.1 ꢁC; [a]D23 +63.71 (c 1.78,
CH2Cl2); nmax (film)/cmꢀ1 2991w, 2945m and 2832w (C–
H), 1730s (C]O); dH (300 MHz; CDCl3) 1.28 and 1.39
(2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.22 and 3.33 (2ꢂ3H, 2ꢂs,
2ꢂacetal OCH3), 3.95 (1H, dd, J 11.0, 3.7, C(4)H), 4.03
(1H, dd, J 6.0, 3.7, C(3)H), 4.54 (1H, dd, J 11.0, 8.2,
C(5)H), 4.70 (1H, d, J 11.3, OCHaHbPh), 5.08 (1H, d, J
11.3, OCHaHbPh), 5.94 (1H, d, J 8.2, C(6)H), 6.65 (1H, d,
J 6.0, C(2)H), 7.30–7.76 (8H, m, aromatic CH), 8.16 (2H,
d, J 8.5, benzoyl o-CH); dC (75.4 MHz; CDCl3) 18.0
(2ꢂbutyl CH3, coincident), 48.0 and 48.3 (2ꢂacetal
OCH3), 67.5 (C(5)H), 69.1 (C(4)H), 73.8 (C(3)H), 74.0
(benzyl CH2), 75.4 (C(6)H), 99.3 and 99.6 (2ꢂacetal C),
102.7 (C(1)), 128.1, 128.6, 128.66, 128.70, 130.3 and
133.5 (aromatic CH), 130.1 & 138.8 (aromatic ipso-C),
138.7 (C(2)H), 165.6 (C]O); m/z (+ve ion electrospray)
603 ([M+Na]+, 100%) (Found 603.0855, C26H29O7INa
([M+Na]+) requires 603.0850).
4.1.7. (20S,30S,3R,4R,5S)-1-Methoxycarbonyl-3-O-ben-
zyl-4-O,5-O-(20,30-dimethoxybutane-20,30-diyl)-6,6-
difluoro-cyclohex-1-ene-3,4,5,-triol
(30).
Palladium
acetate (0.5 mg, 0.002 mmol), tri-2-furylphosphine (1.2 mg,
0.005 mmol) and CH3OH (0.17 mL) were placed in a
three-necked, pear-shaped flask fitted with two Suba SealsÒ
and a balloon filled with CO. Diisopropylethylamine
(0.016 mL, 0.094 mmol) and a solution of the vinyl iodide
24 (0.044 g, 0.09 mmol) in DMF (1 mL) were added to the
flask. CO was bubbled through the solution for 5 min and
the whole system was then flushed several times with CO.
The reaction mixture was stirred under a balloon atmosphere
of CO at room temperature for 24 h. Diethyl ether (10 mL)
and water (5 mL) were then added to the flask. The organic
phase was collected and washed with water (3ꢂ5 mL),
dried (MgSO4) and concentrated in vacuo. Purification by
flash column chromatography (SiO2; EtOAc/petroleum
ether (40–60), 1:19) gave the title compound as colourless
crystals (0.021 g, 56%). Rf 0.37 (EtOAc/petroleum ether
(40–60), 1:4); mp 133 ꢁC; [a]D19 +2.9 (c 1.36, CH2Cl2); nmax
4.1.6. (20S,30S,3R,4R,5S)-1-Iodo-3-O-benzyl-4-O,5-O-
(20,30-dimethoxybutane-20,30-diyl)-6,6-difluoro-cyclohex-
1-ene-3,4,5-triol (24). A sample of the enone 21 (0.160 g,
0.34 mmol) was cooled to 0 ꢁC under an atmosphere of
nitrogen and [bis-(2-methoxyethyl)]-aminosulfurtrifluoride
(DeoxoFluorÒ) (0.94 mL, 5.1 mmol) was carefully added.
The reaction mixture was allowed to warm to room temper-
ature and was stirred for 72 h before being diluted with
CH2Cl2 (100 mL) and quenched by the careful addition of
a saturated aqueous solution of sodium bicarbonate
(100 mL). The organic phase was collected and combined
with three subsequent CH2Cl2 extracts (3ꢂ100 mL). The
combined organic extracts were dried (MgSO4) and concen-
trated in vacuo to give the crude product as a brown oil. Pu-
rification by flash column chromatography (SiO2; EtOAc/
petroleum ether (40–60), 1:19) gave the title compound as

5106
J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
(film)/cmꢀ1 1733s (C]O); dH (400 MHz; CDCl3) 1.39 and
1.43 (2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.30 and 3.36 (2ꢂ3H,
2ꢂs, 2ꢂacetal OCH3), 3.82 (3H, s, CO2CH3), 3.96 (1H, dd,
J 10.8, 3.8, C(4)H), 4.25 (1H, dd, J 5.8, 3.8, C(3)H), 4.50
(1H, dt, J 13.6, 10.8, C(5)H), 4.68 (1H, d, J 11.2,
OCHaHbPh), 5.05 (1H, d, J 11.2, OCHaHbPh), 7.08 (1H,
dd, J 5.8, 2.4, C(2)H), 7.29–7.40 (3H, m, aromatic m- and
p-CH), 7.45 (2H, d, J 7.6, aromatic o-CH); dC (75.4 MHz;
CDCl3) 17.90 and 17.96 (2ꢂbutyl CH3), 48.4 and 48.5
(2ꢂacetal OCH3), 52.8 (CO2CH3), 66.9 (dd, J 21.3, 18.4,
C(5)H), 67.1 (dd, J 6.0, 1.2, C(4)H), 70.1 (C(3)H), 74.8 (ben-
zyl CH2), 99.6 and 99.8 (2ꢂacetal C), 115.9 (t, J 245.1,
C(6)F2), 128.3, 128.6 and 128.7 (aromatic CH), 129.1 (dd,
J 26.5, 22.9, C(1)), 138.4 (aromatic ipso-C), 141.3 (t, J 6.6,
C(2)H), 163.2 (t, J 1.4, C]O); dF (376.3 MHz; CDCl3)
ꢀ106.5 (1F, ddd, J 278.3, 10.8, 2.4, one of C(6)F2),
ꢀ107.4 (1F, dd, J 278.3, 13.6, one of C(6)F2); m/z (CI/
NH3) 446 (MNH+4, 100%), 414 (25), 340 (52), 188 (25),
102 (67) (Found 446.1987, C21H30F2NO7 (MNH+4) requires
446.1990).
temperature in a mixture of water and TFA (1:6, 1 mL) for
3 h and the solvent was then removed directly in vacuo. After
storage under high vacuum for several hours, the title com-
pound was obtained in a sufficiently pure state (assessed
1
by H NMR analysis) to be carried on directly to the final
step (0.016 g,wquant.). dH (300 MHz; CDCl3) 3.89 (3H, s,
CO2CH3), 4.09–4.14 (1H, m, C(4)H), 4.29 (1H, wq, J 9.0,
C(5)H), 4.37–4.43 (1H, m, C(3)H), 4.79 (2H, s, benzyl
CH2), 7.20 (1H, br s, C(2)H), 7.37–7.48 (5H, m, aromatic
CH); dC (75.4 MHz; CDCl3) 52.8 (CO2CH3), 69.1 (d, J
5.7, C(4)H), 71.5 (dd, J 26.2, 20.7, C(5)H), 71.9 (C(3)H),
73.1 (benzyl CH2), 115.9 (dd, J 245.4, 241.3, C(6)F2),
127.7 (t, J 25.6, C(1)), 128.3, 128.76 and 129.0 (aromatic
CH), 137.1 (aromatic ipso-C), 142.9 (t, J 7.2, C(2)H),
163.30 (C]O).
4.1.11. 6,6-Difluoroshikimic acid (11). The diol 35
(0.016 g) was stirred at 60–70 ꢁC in a mixture of water
and concentrated HCl (1:1, 1 mL) for 12 h. After this time,
the solvent was removed directly in vacuo to give the title
compound in quantitative yield as a viscous, yellow oil.
Analytical material could be obtained by further purification
using reverse phase HPLC [Rainin Dynamax C18
(21.4ꢂ250 mm); eluent: H2O/TFA, 99.9:0.1; UV detection
at 254 nm] to give the title compound as a colourless foam
(0.010 g, 68% from 30). [a]2D5 ꢀ128.0 (c 0.10, H2O); dH
(400 MHz; D2O) 3.78 (1H, ddd, J 9.6, 4.0, 1.6, C(4)H),
3.99 (1H, wdt, J 12.0, 9.6, C(5)H), 4.38 (1H, br t, J 4.0,
C(3)H), 6.91 (1H, dd, J 4.4, 2.0, C(2)H); dC (100 MHz;
D2O) 67.4 (C(3)H), 71.1 (d, J 6.8, C(4)H), 72.5 (dd, J
24.3, 19.9, C(5)H), 119.9 (t, J 241.2, C(6)F2), 145.3 (t, J
7.2, C(2)H), 159.6 (C]O), (C(1) not detected); dF
(376.3 MHz; D2O) ꢀ104.8 (1F, br d, J 278.1, one of
C(6)F2), ꢀ109.3 (1F, dd, J 278.1, 12.0, one of C(6)F2); m/z
(ꢀve ion electrospray) 209 ([MꢀH]ꢀ, 60%), 189 (100)
(Found 209.0270, C7H7F2O5 ([MꢀH]ꢀ) requires 209.0267).
4.1.12. (20S,30S,3R,4R,5S,6S)-1-Iodo-3-O-benzyl-4-O,
5-O-(20,30-dimethoxybutane-20,30-diyl)-cyclohex-1-ene-
3,4,5,6-tetraol (20). The vinyl bromide 13 (0.150 g,
0.35 mmol), copper (I) iodide (4 mg, 0.02 mmol) and potas-
sium iodide (0.087 g, 0.52 mmol) were placed in a flask,
which was evacuated and backfilled with nitrogen five times.
nButanol (3 mL) and N,N0-dimethylethylenediamine
(3.1 mL, 10 mol %) were added and the flask was evacuated
and backfilled with nitrogen a further five times. The stirred
mixture was then heated at 120 ꢁC for 24 h. After cooling to
room temperature, the reaction mixture was diluted with
EtOAc (10 mL) and washed with dilute aqueous ammonia
solution (20 mL) followed by water (3ꢂ10 mL). The
organic phase was dried (MgSO4) and concentrated in vacuo
to give a viscous, dark yellow oil. Purification by flash
column chromatography (SiO2; EtOAc/petroleum ether
(40–60), 1:9) yielded the title compound, contaminated
with <10% of 13, as a pale yellow oil (0.121 g). Rf 0.10
(EtOAc/petroleum ether (40–60), 1:9); nmax (film)/cmꢀ1
3468br, m (O–H), 3027m, 2991m, 2948m, 2926m and
2832m (C–H), 1626w (C]C); dH (300 MHz; CDCl3) 1.36
(6H, s, 2ꢂbutyl CH3), 2.78 (1H, br s, 6-OH), 3.28 and
3.32 (2ꢂ3H, 2ꢂs, 2ꢂacetal OCH3), 3.98 (1H, dd, J 6.0,
3.8, C(3)H), 4.10 (1H, dd, J 10.4, 3.8, C(4)H), 4.34–4.40
(2H, m, C(5)H and C(6)H), 4.60 (1H, d, J 11.1, OCHaHbPh),
5.01 (1H, d, J 11.1, OCHaHbPh), 6.51 (1H, d, J 6.0, C(2)H),
4.1.8. (L)-Shikimic acid (1). Methyl shikimate (32)
(0.024 g, 0.13 mmol) was stirred at 60–70 ꢁC in a mixture
of water and concentrated HCl (1:1, 1 mL) for 12 h. After
this time, the solvent was removed directly in vacuo to give
(ꢀ)-shikimic acid in essentially pure form as a yellow oil.
Analytical material was obtained by purification using
reversephase HPLC [Rainin Dynamax C18 (21.4ꢂ250 mm);
eluent: H2O/formic acid, 99.9:0.1; UV detection at
255 nm] to give the title compound as colourless crystals
(0.019 g, 86%). Mp 182–184 ꢁC (Lit.27 mp 184–186 ꢁC);
[a]2D3 ꢀ186.1 (c 1.07, H2O) (Lit.27 [a]2D5 ꢀ170.0 (c 0.86,
H2O)); dH (300 MHz; D2O) 2.16 (1H, ddt, J 18.2, 6.3, 1.8,
one of C(6)H2), 2.67 (1H, ddt, J 18.2, 5.3, 1.8, one of
C(6)H2), 3.71 (1H, dd, J 8.2, 4.1, C(4)H), 3.97 (1H, ddd, J
8.2, 6.3, 5.3, C(5)H), 4.38 (1H,wt, J 4.1, C(3)H), 6.80 (1H,
wdt, J 4.1, 1.8, C(2)H); dC (75.4 MHz; D2O) 30.5
(C(6)H2), 66.0 (C(3)H), 66.8 (C(5)H), 71.3 (C(4)H), 129.9
(C(1)), 137.6 (C(2)H), 170.3 (C]O); m/z (ꢀve ion electro-
spray) 347 ([M2ꢀH]ꢀ, 60%), 173 ([MꢀH]ꢀ, 100).
4.1.9. 3-epi-Shikimic acid (34). Methyl shikimate (32)
(0.011 g, 0.06 mmol) was stirred at 100 ꢁC in a mixture of
water and concentrated HCl (1:1, 1 mL) for 30 h. After
this time, the solvent was removed directly in vacuo to
give the crude product mixture as a yellow solid. Purification
using reverse phase HPLC [Rainin Dynamax C18
(21.4ꢂ250 mm); eluent: H2O/formic acid, 99.9:0.1; UV
detection at 255 nm] gave the title compound as a colourless
solid (0.0021 g, 21%) as well as para-hydroxy benzoic
acid (0.0016 g, 21%) and (ꢀ)-shikimic acid (0.0008 g,
8%). Data for 34: mp 164–166 ꢁC (Lit.28 mp 164–165 ꢁC);
[a]D21 ꢀ28.0 (c 0.1, H2O) (Lit.28 [a]D ꢀ31.0 (c 0.1, H2O));
dH (300 MHz; D2O) 2.11 (1H, dddd, J 17.2, 10.0, 3.8, 2.9
one of C(6)H2), 2.68 (1H, ddd, J 17.2, 5.9, 1.6, one of
C(6)H2), 3.38 (1H, dd, J 10.0, 8.1, C(4)H), 3.68 (1H, td,
J 10.0, 5.9, C(5)H), 4.17 (1H, dddd, J 8.1, 3.8, 2.2, 1.6,
C(3)H), 6.57 (1H, wt, J 2.5, C(2)H); m/z (ꢀve ion electro-
spray) 347 ([M2ꢀH]ꢀ, 43%), 173 ([MꢀH]ꢀ, 100).
4.1.10. (20S,30S,3R,4R,5S)-1-Methoxycarbonyl-3-O-
benzyl-6,6-difluoro-cyclohex-1-ene-3,4,5-triol (35). The
methyl ester 30 (0.021 g, 0.050 mmol) was stirred at room

J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
5107
7.30–7.47 (5H, m, aromatic CH); dC (75.4 MHz; CDCl3)
18.0 and 18.1 (2ꢂbutyl CH3), 48.3 and 48.4 (2ꢂacetal
OCH3), 65.7 (C(4)H), 65.9 (C(5)H), 74.1 (benzyl CH2),
74.5 (C(3)H), 75.4 (C(6)H), 99.6 and 100.0 (2ꢂacetal C),
101.8 (C(1)), 128.0, 128.5 and 128.6 (aromatic CH), 138.9
(C(2)H), 149.7 (aromatic ipso-C); m/z (CI/NH3) 494
(MNH+4, 5%) (Found 494.1053, C19H29O6IN (MNH+4)
requires 494.1040).
88.6 (d, J 175.7, C(6)HF), 99.2 and 99.7 (2ꢂacetal C),
128.1, 128.5 and 128.6 (aromatic CH), 131.9 (d, J 19.2,
C(1)), 137.3 (d, J 5.4, C(2)H), 138.7 (aromatic ipso-C),
165.3 (C]O); dF (376.3 MHz; CDCl3) ꢀ183.9 (dd, J
49.2, 21.3, C(6)HF); m/z (+ve ion electrospray) 433
(100%, [M+Na]+) (Found 433.1631, C21H27FO7Na
([M+Na]+) requires 433.1633).
4.1.15. (20S,30S,3R,4R,5S,6S)-1-Methoxycarbonyl-3-O-
benzyl-6-fluoro-cyclohex-1-ene-3,4,5-triol (42). The
methyl ester 41 (0.035 g, 0.09 mmol) was stirred vigorously
at room temperature in a mixture of water and TFA (1:9,
2 mL) for 2 h and the solvent was then removed in vacuo.
Purification by flash column chromatography (SiO2;
EtOAc/petroleum ether (40–60), 1:2) gave the title com-
pound as an oily half-solid (0.018 g, 72%). Rf 0.17
(EtOAc/petroleum ether (40–60), 1:2); [a]2D4 ꢀ128.6 (c
0.87, CHCl3); nmax (film)/cmꢀ1 3432br (O–H), 2925m (C–
H), 1726s (C]O); dH (300 MHz; CDCl3) 2.46 (2H, br s,
4-OH and 5 O–H), 3.67 (1H, dd, J 9.4, 4.1, C(4)H), 3.86
(3H, s, CO2CH3), 4.17–4.31 (2H, m, C(3)H and C(5)H),
4.72 (1H, d, J 11.6, OCHaHbPh), 4.82 (1H, d, J 11.6,
OCHaHbPh), 5.26 (1H, dd, J 48.5, 6.2, C(6)HF), 6.99 (1H,
d, J 5.0, C(2)H) 7.34–7.42 (5H, m, aromatic CH); m/z (+ve
ion electrospray) 319 (100%, [M+Na]+) (Found 319.0950,
C15H17FO5Na ([M+Na]+) requires 319.0952).
4.1.13. (20S,30S,3R,4R,5S,6R)-1-Iodo-3-O-benzyl-4-O,5-
O-(20,30-dimethoxybutane-20,30-diyl)-6-fluoro-cyclohex-
1-ene-3,4,5-triol (40). DAST (0.06 mL, 0.49 mmol) was
added under an atmosphere of nitrogen to a stirred solution
of the allylic alcohol 20 (0.107 g, 0.22 mmol) in anhydrous
CH2Cl2 (3 mL) at ꢀ78 ꢁC. The stirred reaction mixture was
allowed to warm to room temperature, and stirring was con-
tinued for a further 2.5 h. The reaction mixture was then
cooled to ꢀ20 ꢁC and CH3OH (10 mL) was gradually added
followed by calcium carbonate and the mixture was then
filtered. Concentration of the filtrate in vacuo gave a dark
yellow viscous oil, which was purified by flash column
chromatography (SiO2; EtOAc/petroleum ether (40–60),
1:9) to give the title compound as a colourless oil (0.057 g,
38% from 13). Rf 0.38 (EtOAc/petroleum ether (40–60),
1:9); [a]2D6 +52.0 (c 1.5, CH2Cl2); nmax (film)/cmꢀ1 2992–
2883m (C–H), 1624w (C]C); dH (300 MHz; CDCl3) 1.39
and 1.41 (2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.32 and 3.39
(2ꢂ3H, 2ꢂs, 2ꢂacetal OCH3), 3.79 (1H, ddd, J 11.0, 3.7,
0.7, C(4)H), 3.96 (1H, dd, J 6.0, 3.7, C(3)H), 4.54 (1H,
ddd, J 18.3, 11.0, 7.3, C(5)H), 4.66 (1H, d, J 11.4,
OCHaHbPh), 4.88 (1H, ddd, J 50.1, 7.3, 1.2, C(6)HF), 5.02
(1H, d, J 11.4, OCHaHbPh), 6.62 (1H, dd, J 6.0, 1.2,
C(2)H), 7.33–7.49 (5H, m, aromatic CH); dC (75.4 MHz;
CDCl3) 17.9 (2ꢂbutyl CH3, coincident), 48.3 and 48.4
(2ꢂacetal OCH3), 67.6 (d, J 13.1, C(5)H), 68.2 (d, J 8.7,
C(4)H), 73.6 (C(3)H), 73.8 (benzyl CH2), 93.1 (d, J 182.0,
C(6)H), 99.2 and 99.6 (2ꢂacetal C), 100.6 (d, J 22.5,
C(1)), 128.0, 128.5 and 128.6 (aromatic CH), 138.7 (aro-
matic ipso-C), 139.2 (d, J 4.6, C(2)H); dF (376.3 MHz;
CDCl3) 172.2 (dd, J 50.1, 18.3, C(6)HF); m/z (+ve ion
electrospray) 501 ([M+Na]+, 70%) (Found 501.0549,
C19H24FIO5Na ([M+Na]+) requires 501.0545).
4.1.16. (6S)-6-Fluoroshikimic acid (5). The diol 42
(0.018 g, 0.06 mmol) was stirred at 60–70 ꢁC in a mixture
of water and concentrated HCl (1:1, 1.5 mL) for 10 h. After
this time, the solvent was removed directly in vacuo to give
the title compound as a viscous oil. Purification using reverse
phase HPLC [Rainin Dynamax C18 (21.4ꢂ250 mm); elu-
ent: H2O/formic acid, 99.98:0.02; UV detection at 254 nm]
followed by lyophilisation gave the title compound as a col-
ourless solid (0.071 g, 61%). [a]2D4 ꢀ28.7 (c 0.71, H2O); dH
(300 MHz; D2O) 3.64 (1H, dd, J 9.6, 3.9, C(4)H), 4.01 (1H,
ddd, J 18.0, 9.6, 5.8, C(5)H), 4.39 (1H, wtd, J 4.5, 1.5,
C(3)H), 5.10 (1H, dd, J 48.6, 5.8, C(6)HF), 6.83 (1H, d, J
4.8, C(2)H); dC (100 MHz; D2O) 64.9 (d, J 2.3, C(3)H),
68.2 (d, J 7.6, C(4)H), 69.6 (d, J 20.6, C(5)H), 89.6 (d, J
169.4, C(6)HF), 139.1 (d, J 6.0, C(2)H), 168.4 (C]O),
(C(1) not detected); dF (376.3 MHz; D2O) ꢀ176.5 (dd,
J 48.6, 18.0, C(6)HF); m/z (ꢀve ion electrospray) 191
([MꢀH]ꢀ, 100%), 171 (82) (Found 191.0357, C7H8FO5
([MꢀH]ꢀ) requires 191.0361).
4.1.14. (20S,30S,3R,4R,5S,6S)-1-Methoxycarbonyl-3-
O-benzyl-4-O,5-O-(20,30-dimethoxy-butane-20,30-diyl)-
6-fluoro-cyclohex-1-ene-3,4,5,-triol (41). An identical
procedure to that used in Section 4.1.7 was used to transform
the vinyl iodide 40 (0.070 g, 0.17 mmol). Purification by
flash column chromatography (SiO2; Et2O/petroleum ether
(40–60), 1:1) gave the title compound as a colourless solid
(0.035 g, 58%). Rf 0.28 (Et2O/petroleum ether (40–60),
1:1); mp 113–115 ꢁC; [a]D19 +34.5 (c 1.08, CHCl3); nmax
(film)/cmꢀ1 1730s (C]O); dH (300 MHz; CDCl3) 1.47
and 1.49 (2ꢂ3H, 2ꢂs, 2ꢂbutyl CH3), 3.38 and 3.47
(2ꢂ3H, 2ꢂs, 2ꢂacetal OCH3), 3.69 (1H, dd, J 11.4, 3.4,
C(4)H), 3.89 (3H, s, CO2CH3), 4.20 (1H, dd, J 6.0, 3.4,
C(3)H), 4.57 (1H, ddd, J 21.3, 11.4, 7.1, C(5)H), 4.73 (1H,
d, J 11.4, OCHaHbPh), 5.05 (1H, d, J 11.4, OCHaHbPh),
5.38 (1H, dd, J 49.2, 7.1, C(6)HF), 6.91 (1H, d, J 6.0,
C(2)H), 7.34–7.51 (5H, m, aromatic CH); dC (75.4 MHz;
CDCl3) 17.9 and 18.0 (2ꢂbutyl CH3), 48.3 and 48.4
(2ꢂacetal OCH3), 52.5 (CO2CH3), 68.1 (d, J 4.6, C(4)H),
68.3 (d, J 8.1, C(5)H) 70.6 (C(3)H), 74.1 (benzyl CH2),
Acknowledgements
We acknowledge, with thanks, the EPSRC for funding
(J.L.H., D. J.L. & K.A.W.) and we wish to acknowledge
the EPSRC National Mass Spectrometry Service Centre in
Swansea for the provision of high resolution mass measure-
ments. We are particularly grateful to Professor Derek Boyd
of the Queens University in Belfast for the generous dona-
tion of diol 16, to Professor Gareth Morris and Mr. Gareth
Smith for expert assistance with various vital NMR experi-
ments and to Rehana Sung for assistance with HPLC purifi-
cation of compounds 11 and 5. We also thank AstraZeneca
plc for the generous donation of an authentic sample of
(6S)-6-fluoroshikimic acid.

5108
J. L. Humphreys et al. / Tetrahedron 62 (2006) 5099–5108
Belfast. For further details, contact Professor Derek Boyd,
References and notes
The School of Chemistry, The Queens University of Belfast,
David Keir Building, Stranmills Road, Belfast BT9 5AG,
Northern Ireland.
1. (a) Begum, L.; Box, J. M.; Drew, M. G. B.; Harwood, L. M.;
Humphreys, J. L.; Lowes, D. J.; Morris, G. A.; Redon, P. M.;
Walker, F. M.; Whitehead, R. C. Tetrahedron 2003, 59, 4827;
(b) Humphreys, J. L.; Lowes, D. J.; Wesson, K. A.; Whitehead,
R. C. Tetrahedron Lett. 2004, 45, 3429; (c) Begum, L.; Drew,
M. G. B.; Humphreys, J. L.; Lowes, D. J.; Russi, P. R.; Whitby,
H. L.; Whitehead, R. C. Tetrahedron Lett. 2004, 45, 6249.
2. (a) Sutherland, J. K.; Watkins, W. J.; Bailey, J. P.; Chapman,
A. K.; Davies, G. M. J. Chem. Soc., Chem. Commun. 1989,
1386; (b) Bowles, S.; Campbell, M. M.; Sainsbury, M.; Davies,
G. M. Tetrahedron Lett. 1989, 30, 3711; (c) Sutherland, J. K.;
Whitehead, R. C.; Davies, G. M. J. Chem. Soc., Chem. Com-
mun. 1993, 464; (d) Duggan, P. J.; Parker, E.; Coggins, J.;
Abell, C. Bioorg. Med. Chem. Lett. 1995, 5, 2347; (e) Song,
C.; Jiang, S.; Singh, G. Tetrahedron Lett. 2001, 42, 9069.
3. Davies, G. M.; Barrett-Bee, K. J.; Jude, D. A.; Lehan, M.;
Nichols, W. W.; Pinder, P. E.; Thain, J. L.; Watkins, W. J.;
Wilson, R. G. Antimicrob. Agents Chemother. 1994, 38, 403.
4. Jude, D. A.; Ewart, C. D. C.; Thain, J. L.; Davies, G. M.;
Nichols, W. W. Biochim. Biophys. Acta 1996, 1279, 125.
5. Balasubramanian, S.; Davies, G. M.; Coggins, J. R.; Abell, C.
J. Am. Chem. Soc. 1991, 113, 8945.
11. Hudlicky, T.; Price, J. D.; Rulin, F.; Tsunoda, T. J. Am. Chem.
Soc. 1990, 112, 9439.
12. Simas, A. B. C.; Pais, K. C.; da Silva, A. A. T. J. Org. Chem.
2003, 68, 5426.
13. For a review see: David, S.; Hanessian, S. Tetrahedron 1985,
41, 643.
14. For a review see: Ley, S. V.; Baeschlin, D. K.; Dixon, D. J.;
Foster, A. C.; Ince, S. J.; Priepke, H. W. M.; Reynolds, D. J.
Chem. Rev. 2001, 101, 53.
15. Mancuso, A. J.; Swern, D. Synthesis 1981, 165.
16. Mitsunobu, O. Synthesis 1981, 1.
17. Box, J. M.; Harwood, L. M.; Whitehead, R. C. Synlett 1997,
571.
18. Cacchi, S.; Morera, E.; Ortar, G. Tetrahedron Lett. 1985, 26,
1109.
19. Eykmann, J. F. Chem. Ber. 1891, 24, 1278.
20. For examples of acid mediated removal of benzyl protecting
groups, see: (a) Baker, W.; Brown, N. C. J. Chem. Soc. 1948,
2303; (b) Kametani, T.; Yagi, H.; Satoh, F.; Fukumoto, K.
J. Chem. Soc. 1968, 271; (c) Marsh, J. P.; Goodman, L.
J. Org. Chem. 1965, 30, 2491.
6. Bulloch, E. M. M.; Jones, M. A.; Parker, E. J.; Osborne, A. P.;
Stephens, E.; Davies, G. M.; Coggins, J. R.; Abell, C. J. Am.
Chem. Soc. 2004, 126, 9912.
21. Haslam, E. Shikimic Acid, Metabolites and Metabolism; Wiley:
Chichester, UK, 1993.
22. Bentley, R. Crit. Rev. Biochem. Mol. Biol. 1990, 25, 307.
23. Klapars, A.; Buchwald, S. L. J. Am. Chem. Soc. 2002, 124,
14844.
7. McConkey, G. A. Antimicrob. AgentsChemother. 1999, 43, 175.
8. Lal, G. S.; Pez, G. P.; Pesaresi, R. J.; Prozonic, F. M.; Cheng, H.
J. Org. Chem. 1999, 64, 7048.
24. Kowalski, C. J.; Weber, A. E.; Fields, K. W. J. Org. Chem.
1982, 47, 5088.
25. Luche, J. L. J. Am. Chem. Soc. 1978, 100, 2226.
26. (a) Middleton, W. J. J. Org. Chem. 1975, 40, 574; (b) Hudlicky,
M. Org. React. 1988, 35, 513.
27. Fleet, G. W.; Shing, T. K. M.; Warr, S. M. J. Chem. Soc., Perkin
Trans. 1 1984, 905.
28. Brettle, R.; Cross, R.; Frederickson, M.; Haslam, E.; Mac-
Beath, F. S. Tetrahedron 1996, 52, 10547–10556.
9. For some useful reviews see: (a) Boyd, D. R.; Sheldrake, G. N.
Nat. Prod. Rep. 1998, 15, 309; (b) Hudlicky, T.; Gonzalez, D.;
Gibson, D. T. Aldrichimica Acta 1999, 32, 35; (c) Boyd, D. R.;
Sharma, N. D.; Allen, C. C. R. Curr. Opin. Biotechnol. 2001,
12, 564; (d) Johnson, R. A. Org. React. 2004, 63, 117; (e)
Boyd, D. R.; Bugg, T. Org. Biomol. Chem. 2006, 4, 181.
10. The diol 16 was generously donated by Professor Derek Boyd
at The Queens University of Belfast. It is commercially avail-
able from the QUESTOR Centre at the Queens University of